Historically, "mini" or "reed" relays are extensively used in memory and gate-array testing systems. These relays are critical in testing semiconductor devices because any increase in resistance (i.e., greater than two ohms) on a relay contact will indicate a faulty connection which causes the semiconductor device being tested to be initially rejected as faulty. Time is wasted re-testing the semiconductor device to determine that the test equipment and not the semiconductor device is at fault. Especially troublesome are relays with "intermittent" failures which occur randomly, because the faulty relay generally cannot be located with a high degree of certainty. In the past, troubleshooting technicians and engineers have used several techniques to attempt to locate relays having intermittent faults. Two of these techniques are the "remove-and-replace" technique and the "bench-repair" technique.
In the "remove-and-replace" technique the troubleshooter through diagnosis of the reported tester malfunction narrows the search for the source of the malfunction to a localized area of the test equipment. The repair person then removes a relay which is thought to be at fault and replaces it with a new relay. If this does not cure the malfunction, it is common to remove and replace additional relays, until the malfunction is eliminated. The removal and replacement of each relay may include time consuming desoldering and soldering.
The "bench-repair" technique requires a power supply, voltmeter, ohmmeter, and several test leads or patch cords. In this technique, the relay suspected of fault is connected by test leads or patch cords to external devices and the suspected relay is statically tested by switching the power to the relay coil on and off and reading an ohm meter connected across the relay contacts. Relays which do not operate according to their input or show a high resistance across their contacts are replaced.
When random intermittent relay failures exist, but the faulty relay cannot be located, significant time and effort is expended to "remove and replace" or "bench-repair" relays which may or may not be at fault, without guaranteed results.